Repeater-testing  arrangement



W. H. HARDEN.

REPEATER TESTING ARRANGEMENT.

APPLICATION man MAYIG, 1919.

Patented Jan. 24,1922.

ATTORNEY WiYYZEZM UNITED STATES hATQENT OFFICE.

WILLIAM H. HARDEN, OF BROOKLYN, NEW YORK, ASSIGNOB TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

REPEATER-TESTING .ERBANGEMENT.

Application filed May 16,

known in the art and suitable for transmission in either direction, that the line in either direction shall be balanced by an artificial line or network which is designed to have so far as practicable the same impedance and capacity as the line itself. V Under conditions existing in actual practice however it is impossible to obtain an absolutely perfect balance between the line and the artificial line or network, and if the degree of unbalance becomes great enough in any particulaar case there will be sufficient of the output current from one of the repeaters shunting into the input circuit-of the other repeater and being repeated thereby back to the first repeater, to start a circulation of energy in the repeater circuit that will set' up an action therein known as singing, which action will prevent the effective transmission of speech over the circuit. Furthermore, considerable distortion of the voice currents may be introduced by a condition of unbalance although the gains are not large enough to cause singing. The tendency of the repeaters to sing or cause dis-- tortion because of unbalance in the circuit may be reduced by adjusting the repeaters for lower gains in transmissiomor in other Words to cause them to operate with a smaller degree of amplification. It is,thercfore evident that one of the primary disadvantages of a condition of unbalance. in a Specification of Letters Patent.

Patented Jan. 24, 1922.

1919. .Serial No. 297,517.

shall be more accurate and sensitive than former arran ements, and whereby smaller degrees than heretofore of unbalance may be detected and measured.

In former methods of measuring or detecting a condition of unbalance in a re peater circuit the output circuit of one of the repeaters would be disassociated from the opposite line section and would be associated with the same line section as the input circuit of that repeater. The operators listening or supervising set would now be connected with the line and the gain of the repeater would be increased step by step until the operator could note the occurrence of singing in the apparatus. A relationship has been established between the reach ing on the potentiometer, or other mean for increasing the repeater gain when singing is observed and the degree of unbalance between the line and network which served as' a means for measuring the latter. Such a method has proved satisfactory in rapidly determining the existence of large unbalances, but has not been sufficiently sensitive to prove useful in detecting small unbalances, such as those usually encountered where oi'lice equipment is involved. This is due to the fact that the gain given by one repeater element alone would not be sufliciently large to cause the apparatus to sing where relatively small unbalance of such a type was involved. In the improved testing arrangement of this invention both of the repeater elements are connected during the test in tandem. Such an arrangement utilizes the gain from both repeater elements to such an extent as to extend the range of the test to detect and measure unbalances of much smaller magnitude than previously.

Other features of the invention will be clear from the following detailed description of the arrangement.

In the drawing is shown a circuit diagram of a transimssion line including repeater apparatus. wherein the arrangements ofthis invention are embodied. Connected to section L or a transmission line is the inputcircuit of a vacuum bulb repeater A In the input circuit is included the potentiometer P whereby the gain of the repeater may be adjusted to different degrees. The output circuit of repeater A is inductively related by the three winding transformer 2 to another section or" the transmission line,

such as L Connected to section L of the line is the input circuit of a vacuum'bulb repeater A in which input circuit is included the potentiometer P, whereby the gain of the repeater A, may be adjusted to different degrees. The output circuit of repeater A, is inductively related to line L by means of the three winding transformer 1. \Vhile the repeater elements A and A have been illustrated as of the vacuum bulb type, it is understood that other types of repeaters such as the well known mechanical repeater may be employed. If mechanical repeaters were employed there would be substituted for the potentiometers P and P adjustable .rheostats for regulating the gains of the repeaters. The jacks J and J associated with the repeater set are commonly termed repeater line jacks and serve as means whereby the repeater set may be connected to different lines or testing apparatus. The jacks J 3 and J commonly termed repeater network jacks serve as a means for associating with the repeater any desired networks or testing apparatus. The networks N and N are shown associated with the repeater set and are adapted to balance the line sections L and L respectivel-y.

If for purposes of illustration it is desired .to test and measure the condition of balance between a line, such as L and its balancing network, such as N,, the repeater set will be disconnected from the line L by inserting a short circuit plug (not shown) in repeater line jack J The network N will be disconnected from the repeater set by inserting an open circuit plug (not shown) in the repeater network jack J This operation will so arrange the transformer 2 that the left hand line windingsthereof will operate substantially as an ordinary repeating coil and thus connect the outputcircuit of repeater A to the input circuit of repeater A Accordingly the energy initially transmitted from the line L will be transmitted through the repeater A through the transformer 2, through the repeater .A and thence to transformer 1. If a perfect condition of balance existed between line L, and network N none of this energy would be transmitted from transformer 1 back into the input circuit of repeater A and no continuous circulation (if-energy would take place in the repeater set. However under actual conditions it is practically impossible to provide this condition of perfect balance between the line and network. Accordingly a portion of the enlimited by the characteristics of the re- )eater elements and associated circuits. This action is known as singing. The re peater set may be caused to sing either by increasing the amplification of the repeater elements or by increasing the unbalance between the line and networks until the singing point is arrived at. F or the purposes of this test the gain of the amplifiers may now be increased by adjusting the potentiometers P .and P until the singing point is arrived at. The operator or attendant by connecting a listening or supervising set (not shown) to the repeater apparatus may ascertain when the singing point has been arrived at. lVhen the singing point has been arrived at the settings on the two potentiometers should be added and the reading noted. This reading, for convenience, may be termed the singing point with plus poling.

The previously mentioned short circuit plug and the. open circuit plug should now be interchanged so that the short circuit plug is in the jack J 3 and the open circuit plug is in jack J It will be seen that this operation will so arrange the transformer 2 that the right hand line windings thereof will operateas a repeating coil and will thus couple the output circuit of repeater A to the input circuit of repeater A,. In this case, however, the direction of the input current of repeater A, is reversed with re spect to its previous condition. In the same manner as previously pointed out the potentiometers P and P should now be adjusted until the singing point is arrived point with plus poling or the singing point with minus poling, obtained as described it has been found in practice that the lower reading has been the more repre sentative and should in all cases be the readingused for testing purposes. To this reading, which will be in mile units, as the potentiometers are calibrated in such units, there should be added six miles. This is to make the results obtained in this test comparable to the results obtained with the former methods of testing unbalance in which but one of therepeater elements was employed and so that the same standards of comparison between the amount of unbalance and the singing point of the repeater may be used in both tests. The explanation for this addition of six miles is as follows: in the ordinary form of repeater circuit the eifective gain obtained from the repeater set is less than the actual gain given by one of the bulbs by an amount equal to approximately six miles due to the fact that in both the inputand output sides.

of the repeater circuit the energyis divided into half; Thetransmission gains for the different potentiometer settings when measured by means of thetesting unit are the efiectivegains as.described-above.v In the case of-the testing arrangements-.of'this invention use is made ofv two bulbswith their associated; potentiometers .while the energy losses correspond; practically .:only to vthe the calibrated potentiometer, settings indi cate and six miles should be added to this reading. The results now obtained will be comparable to the results of former tests with one bulb and the relationship between the degree of unbalance between the line and network and the point at which the repeater sings as indicated by the potentiometer readings will afford a means of measuring the amount of unbalance.

It sometimes happens that the repeater set will not have repeater network jacks such as jacks J and J 6 associated therewith but will have the networks permanently associated with the repeaters. In such arrangements and in cases where it is not convenient to use patches or plugs in the network jacks a slightly different method of testing for unbalance must be used, which is as follows: if, for purposes of illustration, it is desired to test or measure the condition of balance between the line L and the network N,, the repeater will be disconnected from line L by the insertion of a short-circuit plug in the repeater line jack J This will cause the transformer 2 tofunction as a repeating coil and will couple the output circuit of repeater A with the input circuit of repeater A,. In the same manner as previously pointed out the operator or test man will connect a listening or supervising set with the repeater and will now adjust the potentiometers P and P so as to increase the gain of the repeaters, step by step and alternately, until the singing point is arrived at. The settings on both potentiometers will then be added and for convenience may be termed singing point with plus poling.

The test should then be repeated with an open circuit plug inserted in jack J 2 instead of the short circuit plug. This latter reading may for convenience be termed the singing point with minus poling. As in the former test the lower of the two readings will be found to be more representative and should be chosen.

During this second form of test it is to be noted that the network of the line not unremain connected to the repeater set. This causes a loss of approximately six miles; in the repeating coil formed by the output transformer 2 and thus practically offsets the six miles difl'e'rence due to having two bulbs and one transformer as referred to above. It-therefore happens that this secnd form of test gives results which arecomparable with those obtained: Iwiththe earlier type oftest with one bulb, andvaccording'ly itis notvnecessary to add 'six milesto thepotentiometer readings in this case. 1

For determining the balance conditions between the networks Y and line L the procedure is exactly the same as-explained above, except that the repeater line jacks,

such as J and the repeater network jacks,

suchas J are opened orshort-circuited as noted.'

While the arrangements of this invention have been specifically illustrated herein as adapted to test the balance condition of a line and networks with which vacuum bulb repeaters are associated, the testing method herein embodied may be applied equally well, in the case where mechanical repeaters are used. Furthermore while the invention has been disclosed as embodied in certain specific arrangements which have been deemed desirable it is understood that it is capable of embodiment in many and widely varied forms without departing from the spirit of the invention as defined in the ap pended claims.

What I claim is:

1. In a transmission system including two line sections balanced by artificial lines and interconnected by a two-way two-element repeater, the method of testing the condition of balance between one of said line sections and its artificial line, which consists in impressing energy from the output circuit of the repeater element whose input circuit is associated with the line to be tested on the input of the other repeater element, and in increasing the gain of said repeater elements until singing takes place in said repeater set.

2. In a transmission system including two line sections balanced by artificial lines and interconnected by repeaters, said repeaters being associated with transformers and having their input circuits bridged across the midpoints of said transformers and having their output circuits connected to said transformers in such a manner that when a condition of balance exists between said line sections and artificial lines that none of the energy from the output circuit of one of said repeaters will be transmitted through one of said transformers to the input circuit of the other of said repeaters, the method of testing the condition of balance between one of said line sections and its artificial line, which consists in creating a condition of unbalance between the line and network &

terminals off'theitransformer associated with the otherof said lines so that energy from.

. sections, repeater elements for interconnecting, said. line sections, three winding transformers for associating said repeaters with said line sections theinput circuits of said repeaters being. associated with the mid points of two of. said windings I of each-0f said transformers and the output circuits of said repeaters being so related to said windings that when .a condition of balance exists between said line sections and artificial. lines between the :liner and network terminals of the transformerassociated, with oneof said line sections and its artificial line. whereby said transformer windings will operate efficiently as a repeating coil and transmit energystromthe outputaciricuit of one of said repeaters. into the input-circuit of the other repeater;

In testimony whereof, I have signed my name to this specification-this th day of May,'1=919.

WILLIAM 'HABDEN. 

